Steam boiler flue gas waste heat recovery system and control method, device and medium thereof

Abstract

The present application discloses a steam boiler flue gas waste heat recovery system and its control method, device, and medium, and relates to the field of waste heat recovery and utilization technology. The system includes a hot water tank and a cold water tank that are interconnected, a first monitor is provided in the hot water tank, a second monitor is provided in the cold water tank, and the water inlet of the cold water tank is connected to softened water; an asymmetric plate heat exchanger and a circulating pump, the asymmetric plate heat exchanger is arranged on the flue of the steam boiler, a third monitor is provided on the flue, and a fourth monitor is provided on the water channel of the asymmetric plate heat exchanger; a frequency converter and a controller respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and the input end of the frequency converter are provided in the control cabinet, the output end of the frequency converter is connected to the circulating pump, the controller can obtain the monitoring data of each monitor, and use the frequency converter to control the operating frequency of the circulating pump. The system of the present application can maximize the recovery of flue gas waste heat.

Description

Technical Field

[0001] The present application relates to the technical field of waste heat recovery and utilization, and in particular to a steam boiler flue gas waste heat recovery system and a control method, device, and medium thereof. Background Art

[0002] Currently Figure 1 As shown, in the related art, a fin-tube heat exchanger is installed on the flue of a steam boiler, and water in a water tank is extracted by a circulating pump to recover the waste heat of the flue gas. However, this method has the disadvantages of low heat exchange efficiency of the fin-tube and high inlet water temperature, and the circulating water volume cannot be matched with the operating load of the steam boiler in real time, resulting in a low waste heat recovery rate of the flue gas. Summary of the invention

[0003] In view of the above-mentioned defects or deficiencies in the related art, it is desired to provide a steam boiler flue gas waste heat recovery system and a control method, device, and medium thereof, which can maximize the recovery of flue gas waste heat.

[0004] In a first aspect, the present application provides a steam boiler flue gas waste heat recovery system, the steam boiler flue gas waste heat recovery system comprising:

[0005] A water tank, the water tank comprising a hot water tank and a cold water tank which are interconnected, a first monitor being arranged in the hot water tank, a second monitor being arranged in the cold water tank, and a water inlet of the cold water tank being connected to softened water;

[0006] An asymmetric plate heat exchanger and a circulating pump, wherein the asymmetric plate heat exchanger is arranged on the flue of the steam boiler, a third monitor is arranged on the flue, a water inlet of the circulating pump is connected to a water outlet of the cold water tank, a water outlet of the circulating pump is connected to a water inlet of the asymmetric plate heat exchanger, a water outlet of the asymmetric plate heat exchanger is respectively connected to a water outlet of the hot water tank and a water inlet of a boiler feed water pump corresponding to the steam boiler, a fourth monitor is arranged on the waterway of the asymmetric plate heat exchanger, and a water outlet of the boiler feed water pump is connected to the steam boiler;

[0007] A control cabinet is provided with a controller and a frequency converter, the controller is respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and the input end of the frequency converter, the output end of the frequency converter is connected to the circulation pump, and the controller is configured to obtain monitoring data of each monitor and control the operating frequency of the circulation pump by using the frequency converter according to the monitoring data.

[0008] Optionally, in some embodiments of the present application, the first monitor includes a first temperature sensor and a first liquid level transmitter, the second monitor includes a second liquid level transmitter, the third monitor includes a second temperature sensor and a third temperature sensor, the second temperature sensor is located at the flue inlet of the asymmetric plate heat exchanger, and the third temperature sensor is located at the flue outlet of the asymmetric plate heat exchanger, the fourth monitor includes a heat meter arranged on the water outlet pipe of the asymmetric plate heat exchanger, the heat meter has a fourth temperature sensor and a fifth temperature sensor, the fourth temperature sensor is located at the water outlet pipe of the asymmetric plate heat exchanger, and the fifth temperature sensor is located at the water inlet pipe of the asymmetric plate heat exchanger.

[0009] Optionally, in some embodiments of the present application, a flue gas flow direction in the asymmetric plate heat exchanger is opposite to a hot water flow direction.

[0010] Optionally, in some embodiments of the present application, the rated flow rate of the circulating pump exceeds 30% of the rated evaporation capacity of the steam boiler.

[0011] Optionally, in some embodiments of the present application, the control cabinet is also configured with an Internet of Things touch screen and an Internet of Things card.

[0012] In a second aspect, the present application provides a control method for a steam boiler flue gas waste heat recovery system according to any one of the first aspects, the control method comprising:

[0013] Obtaining the actual value of the hot water outlet temperature collected by the fourth monitor;

[0014] According to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature, the operating frequency of the circulation pump is controlled through a PID adjustment mode.

[0015] Optionally, in some embodiments of the present application, the control method further comprises acquiring the flue inlet temperature A'1 collected by the third monitor, and when the flue inlet temperature A'1 ≥ the dew point temperature setting value A2,

[0016] A'3= A2+(A'1- A2)×0.302×B;

[0017] And when the flue inlet temperature A'1 is less than the dew point temperature setting value A2, A'3= A'1;

[0018] Wherein, A'3 represents the set value of the hot water outlet temperature; B represents the percentage of waste heat utilization in the sensible heat section. If the hot water tank level collected by the first monitor is lower than the low liquid level once, the percentage of waste heat utilization in the sensible heat section B increases by 0.5%. If the hot water tank level collected by the first monitor is higher than the high liquid level once, the percentage of waste heat utilization in the sensible heat section B decreases by 0.5%. The limit value of B is 60%~100%; A2=57+C, C represents the dew point temperature deviation. If the hot water tank level collected by the first monitor is lower than the low liquid level once, the dew point temperature deviation C increases by 0.1°C. If the hot water tank level collected by the first monitor is higher than the high liquid level once, the dew point temperature deviation C decreases by 0.1°C. The limit value of C is -1°C~+1°C;

[0019] Correspondingly, the operating frequency D'1 of the circulating pump = the PID output frequency D'2.

[0020] Optionally, in some embodiments of the present application, the control method further comprises obtaining the flue inlet temperature A''1 collected by the third monitor, and when the flue inlet temperature A''1 is ≥57°C,

[0021] A''3= 57+(A''1- 57)×0.302×80%;

[0022] And when the flue inlet temperature A''1 is less than 57°C, A''3= A''1;

[0023] Wherein, A''3 represents the hot water outlet temperature setting value;

[0024] Accordingly, the operating frequency D''1 of the circulating pump = PID output frequency D''2 + frequency compensation value E;

[0025] Wherein, if the hot water tank liquid level collected by the first monitor is lower than the low liquid level once, the frequency compensation value E increases by 0.5 Hz; if the hot water tank liquid level collected by the first monitor is higher than the high liquid level once, the frequency compensation value E decreases by 0.5 Hz.

[0026] In a third aspect, the present application provides a control device for the steam boiler flue gas waste heat recovery system according to any one of the first aspects, the control device comprising:

[0027] an acquisition module, configured to acquire an actual value of the hot water outlet temperature collected by the fourth monitor;

[0028] The control module is configured to control the operating frequency of the circulation pump through a PID adjustment mode according to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature.

[0029] In a fourth aspect, the present application provides a computer-readable storage medium, which stores one or more programs, and the one or more programs can be executed by one or more processors to implement the steps of the control method described in any one of the second aspects.

[0030] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0031] The embodiment of the present application provides a steam boiler flue gas waste heat recovery system and its control method, device, and medium. By setting a hot water tank and a cold water tank that are interconnected, softened water can first enter the cold water tank, and then a circulating pump is used to pass the softened water in the cold water tank into an asymmetric plate heat exchanger for efficient heat exchange with the flue gas to heat the softened water, and then enter the boiler through the steam boiler corresponding to the boiler feed pump, which greatly improves the boiler water temperature and can reduce natural gas consumption. At the same time, the operating frequency of the circulating pump can be adjusted so that the water flow rate can match the boiler load and maximize the recovery of flue gas waste heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is a structural schematic diagram of a steam boiler flue gas waste heat recovery system in the related art;

[0034] Figure 2 A schematic diagram of the relationship between flue gas waste heat and the proportion of low calorific value of fuel gas corresponding to different flue gas temperatures provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of water balance of a steam boiler provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of the structure of a steam boiler flue gas waste heat recovery system provided in an embodiment of the present application;

[0037] Figure 5 A schematic diagram of a heat exchange process of an asymmetric plate heat exchanger provided in an embodiment of the present application;

[0038] Figure 6 A flow chart of a control method for a steam boiler flue gas waste heat recovery system provided in an embodiment of the present application;

[0039] Figure 7 A schematic diagram of a water tank liquid level provided in an embodiment of the present application;

[0040] Figure 8 Provided for the embodiments of this application Figure 4 Schematic diagram of temperature distribution in various parts of the flue gas waste heat recovery system of a steam boiler;

[0041] Fig. 9 It is a schematic diagram of temperature distribution of various parts of the steam boiler flue gas waste heat recovery system in the related technology;

[0042] Fig.10 A structural block diagram of a control device for a steam boiler flue gas waste heat recovery system provided in an embodiment of the present application.

[0043] Reference numerals:

[0044] 1-steam boiler flue gas waste heat recovery system, 11-water tank, 111-hot water tank, 112-cold water tank, T1-first temperature sensor, L1-first liquid level transmitter, L2-second liquid level transmitter, 12-asymmetric plate heat exchanger, 13-circulating pump, T2-second temperature sensor, T3-third temperature sensor, Q-heat meter, T4-fourth temperature sensor, T5-fifth temperature sensor, 14-control cabinet, 141-frequency converter, 2-control device for steam boiler flue gas waste heat recovery system, 21-acquisition module, 22-control module. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0047] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. To facilitate a better understanding of the embodiments of the present application, the relevant background knowledge is now described.

[0048] ① Flue gas characteristics. When a natural gas steam boiler is running, it will discharge a large amount of flue gas into the air. The flue gas contains a huge amount of heat, which will cause heat waste and indirectly waste natural gas. Since the main component of natural gas is methane (CH4), its combustion chemical equation is CH4+2O2=CO2+2H2O, so a large amount of water will be produced during the combustion process and exist in the flue gas in the form of water vapor. According to measurements and calculations, the dew point temperature of steam boiler flue gas is generally around 57°C. At different flue temperatures, the ratio of flue gas waste heat to the low calorific value of gas is Figure 2 As shown in the figure, it can be seen that the latent heat of flue gas accounts for a very large proportion.

[0049] ② Calculation of flue gas heat. The flue gas dew point temperature is about 57℃. The flue gas heat above 57℃ is the sensible heat part, that is, the heat generated when the flue gas drops to 57℃, while the flue gas heat below 57℃ is the latent heat part. Since the heat below 57℃ is very large, it is mainly the latent heat of vaporization of water vapor in the flue gas. At the same time, latent heat recovery needs to take into account heat balance, so the analysis will start from the latent heat part.

[0050] 1) Heat from latent heat: The latent heat of vaporization of water vapor in flue gas is about 10% of the low calorific value of natural gas. Based on the consumption of 80Nm3 of natural gas per ton of water vapor, 3 To calculate, for every ton of water vapor produced, the latent heat of vaporization of water vapor in the flue gas is about 6.7×10 4 Kcal, this part of heat can be recovered to raise the temperature of 1 ton boiler feed water by 67℃. Since the dew point temperature of water in flue gas is about 57℃, the latent heat of vaporization of this part of water vapor can raise the boiler feed water temperature to 57℃ at most, while the boiler feed water temperature is generally above 10℃, and raising it to 57℃ can only recover part of the latent heat of vaporization.

[0051] 2) Heat of sensible heat: All flue gas above 57℃ is sensible heat. For every 1℃ flue gas, 80×11.604×1.25×1.09÷4.1868=302Kcal of heat can be recovered. Since every 1000Kcal of heat can raise 1 ton of boiler feed water by 1℃, 302Kcal of heat can raise 1 ton of boiler feed water by 0.302℃. It should be noted that sensible heat = steam consumption × flue gas volume generated by each cubic meter of gas combustion × flue gas density × flue gas specific heat ÷ (Kcal / KJ conversion coefficient).

[0052] ③ Steam boiler water balance. Figure 3As shown in the figure, after the steam generated by the steam boiler is output, the corresponding new water needs to be added, and the steam boiler also needs to discharge waste water, so the water supply of the steam boiler = steam production + discharge volume. The new water may be all softened water at room temperature, or it may contain some steam condensate. In either case, it can be used to recover the waste heat of the boiler flue gas. However, when steam condensate is recovered, the water temperature is high and the proportion of flue gas waste heat recovery is reduced. Therefore, steam condensate is not considered in the subsequent discussion.

[0053] Below through Figures 4 to 10 The steam boiler flue gas waste heat recovery system and its control method, device and medium provided in the embodiment of the present application are described in detail. Please refer to Figure 4 , which is a structural schematic diagram of a steam boiler flue gas waste heat recovery system provided in an embodiment of the present application, the steam boiler flue gas waste heat recovery system 1 includes (i) a water tank 11, the water tank 11 includes a hot water tank 111 and a cold water tank 112 that are interconnected, a first monitor is provided in the hot water tank 111, a second monitor is provided in the cold water tank 112, and softened water is connected to the water inlet of the cold water tank 112. For example, the first monitor includes but is not limited to a first temperature sensor T1 and a first liquid level transmitter L1, etc., and the second monitor includes but is not limited to a second liquid level transmitter L2, etc. For another example, a connecting pipe is provided between the upper part of the hot water tank 111 and the upper part of the cold water tank 112, and the connecting pipe can facilitate water to flow into the cold water tank 112 when the hot water tank 111 is full of water.

[0054] (ii) an asymmetric plate heat exchanger 12 and a circulating pump 13. The asymmetric plate heat exchanger 12 is arranged on the flue of the steam boiler. A third monitor is arranged on the flue. For example, the third monitor includes but is not limited to a second temperature sensor T2 and a third temperature sensor T3. The second temperature sensor T2 is located at the flue inlet of the asymmetric plate heat exchanger 12, and the third temperature sensor T3 is located at the flue outlet of the asymmetric plate heat exchanger 12. The water inlet of the circulating pump 13 is connected to the water outlet of the cold water tank 112, and the water outlet of the circulating pump 13 is connected to the water inlet of the asymmetric plate heat exchanger 12. For example, the rated flow rate of the circulating pump 13 exceeds 30% of the rated evaporation rate of the steam boiler, thereby ensuring the water flow rate when the steam boiler is operated at maximum load and when discharging sewage. The water outlet of the asymmetric plate heat exchanger 12 is connected to the water outlet of the hot water tank 111 and the water outlet of the hot water tank 112, respectively. The steam boiler corresponds to the water inlet of the boiler feed water pump. The advantage of such a setting is to directly send the heated high-temperature water into the steam boiler as much as possible. If the flow rate of the asymmetric plate heat exchanger 12 is less than the feed water flow rate of the steam boiler, it is supplemented by the hot water tank 111. If the flow rate of the asymmetric plate heat exchanger 12 is greater than the feed water flow rate of the steam boiler, the excess part flows into the hot water tank 111. A fourth monitor is provided on the water channel of the asymmetric plate heat exchanger 12, and the outlet of the boiler feed water pump is connected to the steam boiler. For example, the fourth monitor includes but is not limited to a heat meter Q arranged on the outlet pipe of the asymmetric plate heat exchanger 12. The heat meter Q has a fourth temperature sensor T4 and a fifth temperature sensor T5. The fourth temperature sensor T4 is located at the outlet pipe of the asymmetric plate heat exchanger 12, and the fifth temperature sensor T5 is located at the inlet pipe of the asymmetric plate heat exchanger 12.

[0055] (iii) a control cabinet 14, wherein a controller and a frequency converter 141 are arranged in the control cabinet 14. The controller is respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and the input end of the frequency converter 141, and the output end of the frequency converter 141 is connected to the circulation pump 13. The controller can obtain the monitoring data of each monitor and control the operating frequency of the circulation pump 13 by using the frequency converter 141 according to the monitoring data. For example, the controller is a programmable logic controller (PLC), the temperature sensor and the liquid level transmitter are connected to the controller by hard-wired analog signals (such as cables), and the heat meter is connected to the controller by hard-wired communication. For another example, the control cabinet 14 is also equipped with an Internet of Things touch screen, an Internet of Things card and an electric meter. The Internet of Things touch screen can provide functions such as display and interface operation, and the Internet of Things card (such as a traffic card, a SIM card) can provide Internet access, so that the system can be connected to a cloud server and remotely monitored through a mobile phone application, and the electric meter can measure the power consumption of the system.

[0056] For example, Figure 5As shown, in the asymmetric plate heat exchanger 12 of the embodiment of the present application, the flue gas flow direction is opposite to the hot water flow direction, that is, countercurrent, and the latent heat of the flue gas can heat the hot water to about 57°C at most. It should be noted that the main material of the asymmetric plate heat exchanger 12 is 316L stainless steel, and the cross-sectional area occupied by the flue gas channel in each set of plate tube bundles is 10 times the cross-sectional area occupied by the intermediate water channel. The advantage of this arrangement is that there is enough space for the flue gas to pass smoothly through the wide channel, thereby reducing its resistance loss, maintaining the system balance to the greatest extent possible, not affecting the combustion of the steam boiler, and ensuring efficient heat exchange of the medium.

[0057] The steam boiler flue gas waste heat recovery system provided in the embodiment of the present application is provided with a hot water tank and a cold water tank that are interconnected, so that softened water can first enter the cold water tank, and then a circulating pump is used to pass the softened water in the cold water tank into an asymmetric plate heat exchanger for efficient heat exchange with the flue gas to heat the softened water, and then enters the boiler through the corresponding boiler feed water pump of the steam boiler, thereby greatly improving the boiler water temperature and reducing natural gas consumption. At the same time, the operating frequency of the circulating pump can be adjusted so that the water flow rate can match the boiler load and maximize the recovery of flue gas waste heat.

[0058] Based on the above embodiments, the present application provides a method for Figures 4 to 5 The control method of the steam boiler flue gas waste heat recovery system 1 in the corresponding embodiment. Please refer to Figure 6 , the control method specifically comprises the following steps:

[0059] S101, obtaining the actual value of the hot water outlet temperature collected by the fourth monitor.

[0060] S102, controlling the operating frequency of the circulation pump through a PID adjustment mode according to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature.

[0061] It should be noted that PID regulation is a linear regulation method with proportional, integral and differential effects. It integrates the deviation between the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature into a control quantity according to the dimensions of proportion, integration and differentiation to control the controlled process more accurately. Before obtaining the actual value of the hot water outlet temperature, the embodiment of the present application can also obtain the flue inlet temperature collected by the third monitor. When the flue inlet temperature exceeds the starting temperature setting value, the steam boiler flue gas waste heat recovery system 1 automatically starts and the circulating pump 13 runs. When the flue inlet temperature is lower than the stop temperature setting value, the steam boiler flue gas waste heat recovery system 1 automatically stops and the circulating pump 13 stops running. The stop temperature setting value = the starting temperature setting value - the dead zone setting value. The starting temperature setting value can be set according to the actual flue gas temperature. The dead zone setting value can be 5°C. Furthermore, if the hot water tank level reaches below the pump stop level, an alarm is issued and the steam boiler is controlled to stop. If the cold water tank level reaches below the pump stop level, an alarm is issued and the circulating pump is controlled to stop to ensure safety. The water tank level is as follows: Figure 7 As shown, the liquid level on the right is a reference value. The proportions of different liquid levels can be adjusted according to actual conditions, but the order remains unchanged.

[0062] For example, the control mode in the embodiment of the present application includes but is not limited to the following two modes. For example, the flue inlet temperature A'1 collected by the third monitor is obtained. When the flue inlet temperature A'1 ≥ the dew point temperature setting value A2, it indicates that it belongs to the high temperature operation mode.

[0063] A'3= A2+(A'1- A2)×0.302×B;

[0064] When the flue inlet temperature A'1 is less than the dew point temperature setting value A2, it indicates that it is in low temperature operation mode.

[0065] A'3= A'1;

[0066] Among them, A'3 represents the set value of hot water outlet temperature; B represents the percentage of waste heat utilization in the sensible heat section; A2=57+C, C represents the dew point temperature deviation;

[0067] Correspondingly, the operating frequency D'1 of the circulating pump = PID output frequency D'2.

[0068] It should be noted that, in the process of calculating the percentage of waste heat utilization B in the sensible heat section, if the hot water tank level collected by the first monitor is lower than the low level once, the percentage of waste heat utilization B in the sensible heat section increases by 0.5%, if the hot water tank level collected by the first monitor is higher than the high level once, the percentage of waste heat utilization B in the sensible heat section decreases by 0.5%, and the limit of the percentage of waste heat utilization B in the sensible heat section is 60%~100%. In the process of calculating the dew point temperature deviation C, if the hot water tank level collected by the first monitor is lower than the low level once, the dew point temperature deviation C increases by 0.1°C, if the hot water tank level collected by the first monitor is higher than the high level once, the dew point temperature deviation C decreases by 0.1°C, and the limit of the dew point temperature deviation C is -1°C~+1°C. In other words, this control mode continuously adjusts the percentage of waste heat utilization B in the sensible heat section and the dew point temperature deviation C, so that the flow of the asymmetric plate heat exchanger 12 matches the load of the steam boiler as much as possible, and the hot water reaches the highest outlet temperature, which is equivalent to the highest boiler feed water temperature and the maximum energy saving.

[0069] In addition, if the hot water tank liquid level collected by the first monitor is higher than the upper limit of the liquid level, the frequency converter runs at the minimum frequency (for example, 25Hz, which can be set as needed) until the liquid level reaches the set liquid level value, and if the hot water tank liquid level collected by the first monitor is lower than the lower limit of the liquid level, the frequency converter runs at the maximum frequency (for example, 50Hz, which can be set as needed) until the liquid level reaches the set liquid level value.

[0070] For example, the flue inlet temperature A''1 collected by the third monitor is obtained. When the flue inlet temperature A''1 ≥ 57°C, it indicates that it is in the high temperature operation mode.

[0071] A''3= 57+(A''1- 57)×0.302×80%;

[0072] When the flue inlet temperature A''1 is less than 57℃, it indicates that it is in low temperature operation mode.

[0073] A''3= A''1;

[0074] Among them, A''3 represents the hot water outlet temperature setting value;

[0075] Accordingly, the operating frequency of the circulating pump D''1 = PID output frequency D''2 + frequency compensation value E;

[0076] If the hot water tank level collected by the first monitor is lower than the low level once, the frequency compensation value E increases by 0.5 Hz, and if the hot water tank level collected by the first monitor is higher than the high level once, the frequency compensation value E decreases by 0.5 Hz. In other words, this control mode continuously adjusts the frequency compensation value E to match the flow of the asymmetric plate heat exchanger 12 with the load of the steam boiler as much as possible, so that the hot water reaches the highest outlet temperature, which is equivalent to the highest boiler feed water temperature and the maximum energy saving.

[0077] Similarly, if the hot water tank liquid level collected by the first monitor is higher than the upper limit of the liquid level, the frequency converter runs at the minimum frequency (for example, 25Hz, which can be set as needed) until the liquid level reaches the set liquid level value, and if the hot water tank liquid level collected by the first monitor is lower than the lower limit of the liquid level, the frequency converter runs at the maximum frequency (for example, 50Hz, which can be set as needed) until the liquid level reaches the set liquid level value.

[0078] The test results show that if Figure 8 and Fig. 9 As shown, under the same conditions of softening water temperature of 20°C and steam boiler exhaust temperature of 120°C, the comparison of the operating effects of the two modes is shown in Table 1. The energy saving rate of the steam boiler flue gas waste heat recovery system 1 in the embodiment of the present application is increased by 160%.

[0079] Table 1 Comparison of operation effects of different modes

[0080]

[0081] The control method for a steam boiler flue gas waste heat recovery system provided in an embodiment of the present application adjusts the operating frequency of a circulating pump so that the water flow rate can match the boiler load, and uses the circulating pump to pass the softened water in the cold water tank into an asymmetric plate heat exchanger for efficient heat exchange with the flue gas to heat the softened water, and then enters the boiler through the corresponding boiler feed water pump of the steam boiler, thereby greatly improving the boiler water temperature, reducing natural gas consumption, and maximizing the recovery of flue gas waste heat.

[0082] Based on the above embodiments, the present application provides a method for Figures 4 to 5 The control device of the steam boiler flue gas waste heat recovery system 1 in the corresponding embodiment. Please refer to Fig.10 , the control device 2 comprises:

[0083] An acquisition module 21, configured to acquire an actual value of the hot water outlet temperature collected by the fourth monitor;

[0084] The control module 22 is configured to control the operating frequency of the circulation pump through a PID adjustment mode according to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature.

[0085] It should be noted that, for the description of the same contents in this embodiment as those in other embodiments, reference can be made to the description in other embodiments and will not be repeated here.

[0086] As another aspect, the present application provides a computer-readable storage medium for storing program code, the program code for executing the aforementioned Figure 6 The steps of the control method of the corresponding embodiment.

[0087] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and modules described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0088] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules, which can be electrical, mechanical or other forms. The modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment.

[0089] In addition, each functional module in each embodiment of the present application may be integrated into a processing unit, or each module may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of a software functional unit. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it may be stored in a computer-readable storage medium.

[0090] Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the whole or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the control method of each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0091] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0092] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A steam boiler flue gas waste heat recovery system, characterized in that: The steam boiler flue gas waste heat recovery system (1) comprises: A water tank (11), the water tank (11) comprising a hot water tank (111) and a cold water tank (112) which are interconnected, a first monitor being provided in the hot water tank (111), a second monitor being provided in the cold water tank (112), and a water inlet of the cold water tank (112) being connected to softened water; An asymmetric plate heat exchanger (12) and a circulating pump (13), wherein the asymmetric plate heat exchanger (12) is arranged on a flue of a steam boiler, a third monitor is arranged on the flue, a water inlet of the circulating pump (13) is connected to a water outlet of the cold water tank (112), a water outlet of the circulating pump (13) is connected to a water inlet of the asymmetric plate heat exchanger (12), a water outlet of the asymmetric plate heat exchanger (12) is respectively connected to a water outlet of the hot water tank (111) and a water inlet of a boiler feed water pump corresponding to the steam boiler, a fourth monitor is arranged on the waterway of the asymmetric plate heat exchanger (12), and a water outlet of the boiler feed water pump is connected to the steam boiler; A control cabinet (14), wherein a controller and a frequency converter (141) are arranged in the control cabinet (14), wherein the controller is respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and an input end of the frequency converter (141), and an output end of the frequency converter (141) is connected to the circulation pump (13), and the controller is configured to obtain monitoring data of each monitor and, based on the monitoring data, to control the operating frequency of the circulation pump (13) using the frequency converter (141).

2. The steam boiler flue gas waste heat recovery system according to claim 1, characterized in that: The first monitor includes a first temperature sensor (T1) and a first liquid level transmitter (L1), and the second monitor includes a second liquid level transmitter (L2). The third monitor comprises a second temperature sensor (T2) and a third temperature sensor (T3), wherein the second temperature sensor (T2) is located at a flue inlet of the asymmetric plate heat exchanger (12), and the third temperature sensor (T3) is located at a flue outlet of the asymmetric plate heat exchanger (12). The fourth monitor comprises a heat meter (Q) arranged on the water outlet pipe of the asymmetric plate heat exchanger (12), the heat meter (Q) having a fourth temperature sensor (T4) and a fifth temperature sensor (T5), the fourth temperature sensor (T4) being located on the water outlet pipe of the asymmetric plate heat exchanger (12), and the fifth temperature sensor (T5) being located on the water inlet pipe of the asymmetric plate heat exchanger (12).

3. The steam boiler flue gas waste heat recovery system according to claim 1, characterized in that: The flow direction of the flue gas in the asymmetric plate heat exchanger (12) is opposite to the flow direction of the hot water.

4. The steam boiler flue gas waste heat recovery system according to any one of claims 1 to 3, characterized in that: The rated flow rate of the circulation pump (13) exceeds 30% of the rated evaporation capacity of the steam boiler.

5. The steam boiler flue gas waste heat recovery system according to claim 4, characterized in that: The control cabinet (14) is also equipped with an Internet of Things touch screen and an Internet of Things card.

6. A control method for the steam boiler flue gas waste heat recovery system according to any one of claims 1 to 5, characterized in that: The control method comprises: Obtaining the actual value of the hot water outlet temperature collected by the fourth monitor; According to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature, the operating frequency of the circulation pump is controlled through a PID adjustment mode.

7. The control method according to claim 6, characterized in that: The control method further includes obtaining the flue inlet temperature A'1 collected by the third monitor. When the flue inlet temperature A'1 ≥ the dew point temperature setting value A2, A'3= A2+(A'1- A2)×0.302×B; And when the flue inlet temperature A'1 is less than the dew point temperature setting value A2, A'3= A'1; Wherein, A'3 represents the set value of the hot water outlet temperature; B represents the percentage of waste heat utilization in the sensible heat section. If the hot water tank level collected by the first monitor is lower than the low liquid level once, the percentage of waste heat utilization in the sensible heat section B increases by 0.5%. If the hot water tank level collected by the first monitor is higher than the high liquid level once, the percentage of waste heat utilization in the sensible heat section B decreases by 0.5%. The limit value of B is 60%~100%; A2=57+C, C represents the dew point temperature deviation. If the hot water tank level collected by the first monitor is lower than the low liquid level once, the dew point temperature deviation C increases by 0.1°C. If the hot water tank level collected by the first monitor is higher than the high liquid level once, the dew point temperature deviation C decreases by 0.1°C. The limit value of C is -1°C~+1°C; Correspondingly, the operating frequency D'1 of the circulating pump = the PID output frequency D'2.

8. The control method according to claim 6, characterized in that: The control method further includes obtaining the flue inlet temperature A''1 collected by the third monitor. When the flue inlet temperature A''1 is ≥57°C, A''3= 57+(A''1- 57)×0.302×80%; And when the flue inlet temperature A''1 is less than 57°C, A''3= A''1; Wherein, A''3 represents the hot water outlet temperature setting value; Accordingly, the operating frequency D''1 of the circulating pump = PID output frequency D''2 + frequency compensation value E; Wherein, if the hot water tank liquid level collected by the first monitor is lower than the low liquid level once, the frequency compensation value E increases by 0.5 Hz; if the hot water tank liquid level collected by the first monitor is higher than the high liquid level once, the frequency compensation value E decreases by 0.5 Hz.

9. A control device for a steam boiler flue gas waste heat recovery system as claimed in any one of claims 1 to 5, characterized in that: The control device comprises: an acquisition module, configured to acquire an actual value of the hot water outlet temperature collected by the fourth monitor; The control module is configured to control the operating frequency of the circulation pump through a PID adjustment mode according to the actual value of the hot water outlet temperature and the set value of the hot water outlet temperature.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to implement the steps of the control method described in any one of claims 6 to 8.

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